1. Field of the Invention:
This invention relates to fluidized bed reactors and furnaces, and is particularly directed to a solid-particle reactor employing a vibratory bed for the particles.
2. Description of the Prior Art:
Solid fuel stoves and furnaces have been proposed in which the fuel is introduced therein, for example, on a chain grate. This facilitates automatic stoking and ash or cinder removal, but cannot guarantee complete and efficient combustion. In order to enhance combustibility, forced air is introduced into the bed of solid fuel in the furnace to circulate and provide sufficient oxygen to the burning coals of solid fuel. However, the fuel, as it burns, can become rather compacted, and normally a great deal of pressure is required to ensure adequate air circulation. Even then, the forced air tends to take the path of least resistance through the fuel bed. Consequently, so-called blow holes develop which form channels for the forced air, and the air ceases to reach more compacted masses of fuel apart from the blow holes. Further, the forced air passes more quickly through the blow holes and tends to cool the burning coals, thereby keeping the heating system below maximum heating efficiency.
Additionally, ash removal systems tend to be rather complex and inefficient, and their presence further interferes with the efficient combustion of the solid fuel.
Furthermore, conventional solid fuel heating apparatus, such as wood stoves or stoker coal furnaces, tend to burn dirty, emit considerable smoke, and require frequent cleaning. Such apparatus cannot burn a wide range of fuel types and sizes, and do not operate well if the fuel is wet.
Pulverized coal burners are in common use, especially among electric utilities. These burners inject coal as a fine powder into a combustion chamber, where it is mixed with air and burned. Although these produce more heat with less coal than stokers, they also emit much higher levels of pollution and require large and expensive pollutant-trapping equipment on their exhaust stacks.
Fluidized bed combustion chambers employ a bed of crushed coal covered with a layer of granular material, usually including crushed limestone. Air is forced at rather high pressures up through the bed causing the coal and granular material to "boil" so that the crushed coal particles are suspended in air. Combustion takes place at a relatively low temperatures, so that clumps or clinkers of ash form less frequently and there is far less nitrogen oxide produced. Sulfurous wastes are trapped in the limestone granules.
Unfortunately, these fluidized bed chambers have severe disadvantages. For one thing, the fluidized bed furnaces are large, complex systems that require a significant amount of maintenance, so that a full time monitor is almost always required. Another problem of the fluidized bed burners is their immensity: because the bubbling mixture is sometimes blown more than ten meters into the air, the chambers must be constructed as silos from ten to twenty five meters high, complicating installation at existing factories or plants, and making installation impossible in a home heating plant.
Still another disadvantage is that heat paths or channels (i.e., blow holes) often occur in the fluidized bed. That is, the path of air through the bed will follow the path of least resistance, and often combustion occurs only along certain channels. The blasting of compressed air does not always break up these channels to ensure efficient combustion.
Furthermore, a substantial amount of energy is consumed in compressing the air that must be blasted into the chamber to fluidize the bed.
Fluidized bed reaction chambers also have many applications in the petroleum and chemical process industries.